The present invention relates to a plasma processing device capable of effecting distribution control of the processing speed of a board, when processing the board using gas dissociated by a plasma, for producing a semiconductor element board or a liquid crystal board, and a plasma processing method for processing the board surface using the device.
A conventional plasma processing device, for example, introduces electromagnetic waves from a microwave introduction window into a chamber, forms a magnetic field in a separate processing chamber, and generates a plasma. As a processing device using this plasma, there are an etching device and a CVD device available.
In a conventional microwave plasma generation device, for example, in a microwave plasma device as described in Japanese Patent Application Laid-Open 5-263274, by increasing the distance from the microwave introduction window to the board being processed and diffusing the plasma, the plasma distribution on the board, particularly the ion flux distribution, is made uniform. Furthermore, as described in Japanese Patent Application Laid-Open 6-104210, by installing a plurality of dielectrics in the processing chamber and distributing the microwave which has entered from the window between them, it is possible to make the radical distribution generated by the microwave uniform in the processing chamber.
Furthermore, as disclosed in Japanese Patent Application Laid-Open 6-104210, a shielding plate for shielding the plasma reaction chamber from the microwave plasma generation chamber is installed between the chambers, and the chambers are penetrated by a pore. As disclosed in Japanese Patent Application Laid-Open 7-263348, a plurality of dielectric pieces are arranged on the microwave entry surface of the microwave introduction widow for partitioning the plasma generation chamber and the microwave introduction means so as to control the microwave intensity distribution emitted into the plasma generation chamber. Furthermore, as disclosed in Japanese Patent Application Laid-Open 9-148097, the dielectric window for isolating the electromagnetic wave transmission unit from the discharging chamber is installed in the electromagnetic wave transmission unit and an electromagnetic wave reflection plate is installed on the discharging chamber side of the dielectric window so as to generate a ring-shaped plasma in the discharging chamber.
In a recent semiconductor memory, for example, the 256MD RAM (dynamic random access memory) and subsequent devices, to form a fine contact hole, it is proposed to increase the SiO2/SiN selection ratio in the etching of an SiO2 film, for example, to 20 or more. On the other hand, the diameter of the board (wafer) used to manufacture semiconductor memories increases year by year, and, for example, a wafer 300 mm in diameter is used. When a board having such a large diameter is to be plasma-processed, it is most important to ensure the uniformity of plasma distribution in the radial direction.
When a plasma processing device, for example, a device generating plasma by 450-MHz electromagnetic waves, is compared with a plasma processing device using, for example, 2.45 GHz electromagnetic waves, electromagnetic waves are propagated in the plasma under the conditions of a high electron density of 29 times and a high pressure of 5.4 times. On the other hand, in a higher density and at a higher pressure, the attenuation (absorption) of electromagnetic waves in plasma is larger. Therefore, when 450-MHz electromagnetic waves enter a plasma, they immediately attenuate before they reach the ECR surface. Also, in a lower magnetic field area than the ECR surface, an attenuated electric field exists. Like this, electromagnetic waves are absorbed into the plasma in the neighborhood of the sheath right under the antenna, with the result that a crowning electric field is generated and a crowning power deposition and a resultant crowning electron density distribution are obtained.
According to the aforementioned techniques, when the height of the chamber is decreased, if the power is low, plasma centralized as a whole is not diffused sufficiently in the periphery, so that a failure, in that the ion flux to the board decreases toward the periphery, is generated. In a device having a structure in which an electrode for applying a bias voltage to the wall (quartz window) opposite to the board is installed, the microwave is centralized under the electrode depending on the conditions of the magnetic field, and so a failure is generated in that the plasma density being generated is not uniform in the radial direction.
In the microwave plasma processing device, a structure in which a member for absorbing or a member for reflecting the microwave is fixed and installed in the waveguide, and the electromagnetic field intensity distribution of the microwave which enters, irregularly reflects, and then reenters the plasma generation chamber is made uniform in the plasma generation chamber; a structure in which a plurality of dielectric pieces are arranged on the microwave entry surface of the window, and the microwave intensity distribution emitted into the plasma generation chamber is controlled; and a structure in which a electromagnetic wave reflection plate is installed on the discharging chamber side of the microwave leading-in window material have been proposed. However, when these techniques are applied to a structure in which an electrode is provided at the center, it is changed to a structure wherein the electromagnetic wave reflection plate or dielectric pieces are separated from the electrode surface at the center or to a structure wherein they are separated from the plasma, and so there is a problem in that the effect for strengthening the electric field in the neighborhood of the outer periphery of the electrode is small. When the electromagnetic wave reflection plate or the dielectric pieces are in direct contact with the plasma, the electromagnetic waves are centralized in the corners thereof depending on the kind of gas, and strong plasma is generated locally, and so a problem arises in that the electromagnetic wave reflection plate or dielectric pieces are consumed or worn powder is scattered and contaminates the board.
An object of the present invention is to provide a plasma processing device and a plasma processing method for correcting a non-symmetry of the plasma density distribution relative to the center and for distributing plasma uniformly in the chamber when introducing electromagnetic waves into the chamber and forming plasma and for realizing a uniform processing of the board surface when plasma-processing a board with a large diameter.
To solve the aforementioned problem, the present invention provides a plasma processing device for supplying electromagnetic waves to a first plate, generating plasma in a vacuum atmosphere between the first plate and a second plate which is arranged opposite to it, and processing the board loaded on the second plate, wherein the dielectric window for propagating electromagnetic waves is installed in the outer periphery of the first plate, and, in the window, an electromagnetic wave distribution corrector composed of an electrical conductor or a dielectric is embedded so as to be spaced from the first plate so that at least the side and bottom of the electromagnetic wave distribution corrector are not exposed in the aforementioned vacuum atmosphere.
Another characteristic of the present invention resides in the fact that, in a plasma processing method for supplying electromagnetic waves to the first plate, generating a plasma in the vacuum atmosphere between the first plate and the second plate which is arranged opposite to it, and processing the board loaded on the second plate, the method includes a step of converting the atmosphere in which the board is loaded on the second plate to a vacuum atmosphere, a step of introducing gas into the vacuum atmosphere, a step of introducing electromagnetic waves of 100 to 900 MHz into the vacuum atmosphere via the dielectric window which is installed in the outer periphery of the first plate and in which the electromagnetic wave distribution corrector composed of an electrical conductor or a dielectric is installed so as to be spaced from the first plate and generating a plasma, a step of etching the board loaded on the second plate using the plasma, and a step of taking the board out of the vacuum atmosphere.
According to the present invention, in the window installed in the neighborhood of the outer periphery of the first plate, in order to introduce electromagnetic waves, a substance for changing the scattering of electromagnetic waves, for example, a conductive ring, is inserted, so that the centralization of electromagnetic waves is suppressed and the density distribution of plasma in the radial direction can be controlled. By doing this, when a board with a large diameter is to be plasma-processed, a plasma processing device and a plasma processing method for realizing a uniform processing of the board surface can be provided.